Setting up an under frame mount coupler with WD setup

That thread that I linked to earlier discusses that problem. Many receivers are either too big or not strong enough and wind up when under load. You just have to tilt some more to compensate or find a way to reinforce the hitch receiver to it doesn't bend as much. Many folks (me included) replace the factory receiver with an aftermarket one that is built much stronger. Many mid 2000 GM vehicles were notorious for this and some others also.
Barney